Limits

Ted had limited control over his ability to emit radiation. When agitated, he appeared to emit radiation unintentionally. This radiation was harmful to people in his vicinity. His control did improve with practice, and he appeared to be able to emit radiation on purpose, but he apparently couldn't consistently prevent himself from emitting radiation, especially if angry or injured.

Ted could apparently emit a broad spectrum of electromagnetic radiation, although he had only a limited understanding of the physics involved. He could not choose specifically whether to emit microwaves or gamma rays, but he could choose whether to radiate "hot" energy or "bright" energy. He also appeared to be able to emit neutron radiation, as some objects that have been exposed to him have become radioactive.

At close range, Ted could produce enough radiation to bring a glass of water to a boil or melt a brass door lock in just a few seconds. His uncontrolled emissions set fire to common construction materials from several meters away. He was also capable of emitting an electromagnetic pulse strong enough to disable electronics throughout a large building. An uncontrolled release of radiation can generate a massive explosion similar to that of a nuclear bomb. In an alternate timeline, such an explosion occurred in Kirby Plaza and was powerful enough to destroy most of the skyscrapers in Midtown Manhattan.

Ted appeared to be unharmed by his own radioactive emissions. He caused the deaths of others (reducing people to skeletal remains) during at least two escapes, but never appeared to affect himself. Whether this immunity applies to radiation from other sources is unknown. Additionally, the Company believed that clonazepam could act as a tranquilizer for Ted. However, despite being injected with it, he still blew up the Bennets' home in a massive explosion (Company Man).

When he absorbed this ability from Ted Sprague in The Hard Part after meeting him at Kirby Plaza, he had to intensely concentrate to get this power under control. Before meeting Ted, Peter expressed fear that this ability would be too strong for him to contain. In How to Stop an Exploding Man, he even passed out attempting to do so. During his fight with Sylar, he lost control and was on the verge of exploding, but thanks to Nathan, he was flown high enough to explode without causing any significant damage to anyone other than Nathan who suffered severe radiation burns. Peter himself survived exploding though whether it was due to the nature of this ability or due to Peter being able to regenerate is unclear.

Following Peter's explosion, he gained control over the ability, not losing control over it even when he had no memory and only accessed his powers randomly in general. In Powerless, Peter was able to use this ability to destroy Strain 138 of the Shanti virus and alter the future. In this case, Peter was able to release a blast of radiation between his hands powerful enough to destroy the virus without harming Nathan or Matt who were nearby. He also didn't fall into danger of exploding again.

After taking this ability from Ted , Sylar stands on the roof of a building, conjuring up radiation on command (Landslide). Sylar has never been seen emitting radiation unintentionally, and conjured plumes of smoke shortly after acquiring the ability, whereas Ted took an extended period of time to do the same.

Gabriel becomes enraged after his son is killed by Knox. He channels this ability through his hands when he punches Knox. He begins to lose control of the ability, however, and soon explodes, destroying Costa Verde.

Notes

While Ted, Peter, and Sylar have never been harmed by their own radiation emissions, Amid's hands had visible radiation damage, as seen in a scene in the unaired pilot.

Ted's medical chart from the old Assignment Tracker indicated that the mitochondria in his cells could cause nuclear fusion between deuterium and tritium atoms. The words "hook up w/ Li" are also scribbled in his chart. The nuclear fusion between deuterium and tritium releases a free neutron, which, in some proposed fusion reactors, could be captured by an atom of lithium to produce more tritium.

Occasionally, the eyes of some users of this ability glow orange-red (Godsend, Company Man). This seems to happen when the characters are under extreme emotional duress.

This ability is tied to three of the alternate futures in the Heroes storyline in different ways: the explosion future, the outbreak future and the exposed future. In the latter, Peter's presence in the future causes Future Gabriel to lose control of the ability and destroy Costa Verde, killing 200,000 people. In the explosion future, Sylar originally and Peter after saving Claire exploding causes the future and stopping the explosion alters it. With the outbreak future, Peter alters the timeline by using this ability to destroy the virus that causes said timeline.

Arthur Petrellistole his son Peter's abilities, saying, "I have [your powers] now." (Dying of the Light). It is presumed that Arthur stole all of Peter's abilities, including induced radioactivity. However, it is possible that Arthur did not steal all of Peter's abilities. Since Arthur never used this ability, there is no conclusive evidence that he actually stole this ability.